Osseous anchoring implant with a polyaxial head and method for installing the implant

ABSTRACT

An osseous anchoring implant, various embodiments of which comprise an osseous anchor and a head bearing fixation structure capable of receiving and fixing at least one bar, the head of the implant being traversed by at least one duct, which receives the bar through a lateral aperture, and by a threaded channel, whose axis is not parallel to the axis of the duct, which receives a fixation screw of the bar, the implant being characterized in that it comprises fixation structure of the head on the part of the implant which extends from the osseous anchor, these fixation structures allowing, prior to blocking and fixing, at least a determined mobility of the head around at least one axis not parallel to the axis of symmetry of the osseous anchor. The fixation screw of the bar may comprise a ball and socket at its base.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/570,080, which is a National Stage entry of International Applicationnumber PCT/IB04/02825 filed Sep. 1, 2004, which claims priority toFrench patent application number FR0310363 filed Sep. 1, 2003.

BACKGROUND

The present invention relates to an implant providing osseous anchoragein a vertebra, for example to anchor an osteosynthesis device. Thisimplant has a polyaxial head allowing to receive, in a plurality ofangular positions, a bar linking several implants. The present inventionalso relates to a method for installing the implant, in particular toperform a reduction of a spondylolisthesis (i.e., a jutting out of avertebra with respect to the adjacent vertebrae).

It is known, in the prior art, to fix a plurality of implants, each to avertebra, and to connect them together with a bar or a plate, fixed toeach implant, along the vertebral column, so as to maintain or correctthe rachis. These implants are generally fixed to the vertebrae, eithervia screwing of a threaded part of the implant in a vertebra, or byfixing of a hook of the implant onto a vertebra. The implants known tothe prior art are equipped with a fixation channel, at the head,allowing to fix the bar or plate into a duct. Sometimes, a lateralaperture allows introducing the bar via the side of the duct.

The international patent application WO 03/049629 shows an implant withpolyaxial head allowing to orient the bar in different positions beforefixing it, these positions being restricted by a determined clearance ofthe bar around the axis of the implant and/or around the axis of theduct, thanks to a ball and socket connection. This polyaxial systemallows to simplify the positioning of the bar and to reduce theconstraints exercised by the implant on the bar, but offers a limitednumber of levels of movement (i.e., a limited freedom of motion of thevarious elements of the implant with respect to each other).

On the other hand, the implants known in the prior art generally allowto completely reduce a spondylolisthesis of the rachis but do not allowto partially reduce it, a spondylolisthesis reduction consisting in arepositioning of the vertebra in the axis of the adjacent vertebrae inthe vertebral column. Yet, in some cases, it is necessary to onlypartially reduce a spondylolisthesis or to control, during implantation,the reduction level of the spondylolisthesis.

The international patent application WO 00/15125 mentions that animplant with polyaxial head allowing to orient the bar in differentpositions before fixing it. However, the different embodiments of thisimplant in the prior art have the inconveniences, when the bar isinserted into its duct, of either not offering all the possible levelsof movement, or of not allowing to continue to screw the implant intothe vertebrae.

SUMMARY

The object of the present invention is to overcome these inconveniencesin the prior art by proposing an implant for osseous anchoring allowingto restrict the constraints exercised on the rachis during a correctingof the latter and to control the reduction level of a spondylolisthesis.

This object is reached through an implant of osseous anchoringcomprising a body equipped with osseous anchoring means and a headbearing fixation means capable of receiving and fixing at least one bar,in particular of osteosynthesis, the head of the implant being traversedby at least one duct receiving the bar through a lateral aperture and bya threaded channel having an axis not parallel to the axis of the ductand receiving a fixation screw of the bar, the implant beingcharacterized in that it comprises fixation means of the head on a partof the body of the implant extending along the osseous anchoring means,these fixation means of the head consisting in a portion of the headwhich forms a ring into which is inserted a fixation olive threaded ontothe part of the body of the implant extending along the osseousanchoring means and allowing, prior to blocking and fixing, at least adetermined clearance of the head around at least one axis not parallelto the axis of symmetry of the osseous anchoring means, and in that thefixation screw of the bar comprises a ball and socket at its baseallowing at least a determined clearance of the bar around at least oneaxis parallel to the duct axis, the fixation means of the head and theball and socket of the fixation screw of the bar allowing a determinedclearance of the head around the axis of symmetry of the osseousanchoring means, even when the bar is inserted into the duct.

According to another feature, the inside diameter of the ends of theduct of the head is greater than the inside diameter of the center ofthe duct, which confers a widened out profile to the duct allowing, inassociation with the ball and socket at the base of the fixation screw,a determined clearance of the bar around the axis of the duct.

According to another feature, the head is equipped with a ring, which isplaced on the other side of the head in relation to the duct, and inthat the part of the implant extending along the osseous anchoringmeans, which is threaded through a fixation olive, itself threadedthrough a ring, is cylindrical and threaded and extends, widening outfrom the cylindrical part towards the anchoring means, by a taperedpart, complementary of a tapered internal surface of the fixation olivewhich is sectioned at a point along its entire height.

According to another feature, the external surface of the fixation oliveis convex and complementary of a concave internal surface of the ring,the external diameter of the olive being slightly less than the internaldiameter of the ring, so that the olive, compression inserted into thering thanks to the section of the olive along its entire height, allowsa retaining of the head on the olive, whilst allowing the orientationand the determined clearance of the head around at least one axisparallel to the axis of symmetry of the osseous anchoring means.

According to another feature, a nut has, along its entire height, athreaded drilling intended to be screwed to the cylindrical part of theimplant which is threaded so as to initially provoke, either the rise ofthe body of the implant up to the bar, or the descending of the oliveand the head onto the body of the implant, according to the relativepositions of the head, the olive and the body in relation to the bar,then secondly, the leaning of the olive on the tapered part of theimplant, which engenders the expansion of the fixation olive, and thusthe blocking of the head in the desired position.

According to another feature, the nut is equipped with flats capable ofco-operating with a tool adapted to the screwing of the nut to thethreaded cylindrical part of the implant.

According to another feature, the osseous anchoring means are a hook.

According to another feature, the osseous anchoring means are a threadedpart.

According to another feature, the cylindrical part of the body of theimplant is equipped, at its end opposite the osseous anchoring means,with a blind hole with six faces capable of co-operating with a tooladapted to the screwing of the implant.

According to another feature, the ball and socket of the fixation screwof the bar comprises a flat at its base.

According to another feature, the flat at the base of the ball andsocket of the fixation screw of the bar consists in a disc prominent atthe periphery of the ball and can be used as a stop limiting themovement of the ball in relation to the fixation screw of the bar.

According to another feature, the ball and socket at the base of thefixation screw of the bar is associated with a mobile base locatedbetween the bar and the duct in a housing in the duct, this basefacilitating, prior to blocking and fixing of the bar, the determinedclearance of the bar around at least one axis parallel to the axis ofthe duct.

According to another feature, the mobile base has formal irregularitiesco-operating with formal irregularities of the duct, so as to restrictthe movement of the base in its housing and therefore restrict theclearance of the bar around the axis parallel to the axis of the duct.

Another object of the invention is to propose a method for installingthe implant according to the invention.

This object is reached via a method for preparing out with the bodyprior to the implanting of an osseous anchoring implant comprising athreaded part extended by a smooth tapered part itself extended by athreaded cylindrical part, said cylindrical part being threaded througha fixation olive itself threaded in a head equipped with a ductreceiving an osteosynthesis bar by a lateral aperture and with a channelreceiving a fixation screw provided with a ball and socket at its base,the fixation olive and the head being retained by a nut screwed to thecylindrical part, the ball and socket being provided, at its base, witha flat consisting in a disc which is prominent at the periphery of thebase of the ball and can thus be used as a stop limiting the rotation ofthe ball in relation to the fixation screw, the method beingcharacterized in that it comprises at least the following successivesteps:

the insertion of the bar, via the lateral aperture, into the duct inwhich it is at least retained via a partial screwing of a fixationscrew;

the positioning of the flat at the base of the ball as a stop in theduct, on its internal surface opposite to the lateral aperture, in orderto prevent a rotation of the bar in the duct, thanks to the contact ofthis flat of the ball with a flat on the bar and, consequently prevent,the descending of the head in relation to the bar;

the partial screwing of the nut on the cylindrical part of the implant,so that the nut comes into contact with the fixation olive, so as toprevent a disengagement of the fixation olive and the head from thecylindrical part of the implant, whilst allowing the movement of thehead of the implant around at least the axis of symmetry of the osseousanchoring means, in the expectation of the screwing of the osseousanchoring means which will provoke the rise of the body and thevertebra, followed by the screwing of the nut, which will end the riseof the body and the vertebra and will then block the head and the bodyin the desired position.

According to another feature, the method comprises at least thefollowing successive steps:

the insertion of the bar, via the lateral aperture, into the duct inwhich it is at least retained via a partial screwing of a fixationscrew;

the positioning of the flat at the base of the ball as a stop in theduct, on its internal surface opposite to the lateral aperture, in orderto prevent a rotation of the bar in the duct, thanks to the contact ofthis flat of the ball with a flat on the bar and, consequently prevent,the descending of the head in relation to the bar;

the partial screwing of the nut on the cylindrical part of the implant,so that the nut comes into contact with the fixation olive, so as toretain the vertical position of the cylindrical part of the implant, inrelation to the head, whilst allowing the movement of the head of theimplant around at least the axis of symmetry of the osseous anchoringmeans, in the expectation of the complete screwing of the nut which willprovoke the rise of the body and the vertebra and will then block thehead and the body in the desired position.

According to another feature, the steps of the partial screwing of thefixation screw and the positioning of the flat at the base of the ballas a stop in the duct, on its internal surface opposite to the lateralaperture, can be replaced by a step of a complete screwing of thefixation screw, so as to prevent any movement of the ball and the barand, consequently, prevent the descending of the head in relation to thebar.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Other features and advantages of the present invention will be clearerupon reading the description thereafter with reference to the annexeddrawings, wherein:

FIG. 1 represents a blown-up perspective view of the osseous anchoringimplant according to a first embodiment of the invention;

FIG. 2 represents a side view of the osseous anchoring implant accordingto the embodiment of FIG. 1;

FIG. 3 represents a blown-up perspective view of the osseous anchoringimplant according to another embodiment of the invention;

FIG. 4 represents a side view of the osseous anchoring implant accordingto the embodiment of FIG. 3;

FIG. 5a represents a perspective view of an embodiment of the head ofthe osseous anchoring implant with the section planes B-B and C-C ofFIGS. 5a and 5b , respectively, FIG. 5c also representing the fixationbar and the fixation screw equipped with a ball and socket connection atits base;

FIGS. 6a and 6b represent sectional views, respectively, according tothe axis of the duct and according to an axis perpendicular to the axisof the duct, of the head of the osseous anchoring implant equipped withthe fixation bar and the fixation screw equipped with a ball and socketconnection at its base and associated with a mobile base;

FIG. 7 represents a blown-up perspective view of the osseous anchoringimplant according to another embodiment of invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

The osseous anchoring implant according to the invention comprises fourelements: a body (1), a head (2), a fixation olive (3) and a nut (4).The body (1) of the implant comprises, at its upper end, a cylindricalpart (10) and, at its lower end, osseous anchoring means (11) foranchoring in a vertebra. The cylindrical part (10) is threaded on itsexternal wall. The cylindrical part (10) and the anchoring means (11)are linked via a smooth tapered part (12), whose transversal sectionincreases between the cylindrical part (10) and the anchoring means(11). The weakest section of the tapered part (12) is substantiallyequal to the transversal section of the cylindrical part (10). Thecylindrical part (10), the tapered part (12) and the anchoring means(11) constituting the body (1) of the implant are placed according to afirst axis (A₁).

The head (2) of the implant comprises a duct (20) allowing to receive abar (7), which links several implants together within the context of anosteosynthesis device so as to retain, support or correct the rachiswhen the implants are screwed in vertebrae. The head (2) of the implantis called polyaxial as it has several levels of free movement, thanks tothe fact that it is fixed to the body (1) by a ring (21) clamping afixation olive (3) constituted of a ring with a tapered and smoothinternal wall, complementary of the smooth tapered part (12) of the body(1) of the implant. The external wall of the olive (3) is convex andcomplementary of the internal surface of the fixation ring (21) of thehead (2). This freedom of movement of the head (2), in relation to thebody (1) of the implant, consists in a rotation or a combination ofseveral rotations according to three axes substantially perpendicular toone another, particularly visible in FIG. 2 and passing through thegeometric center of the olive (3). The polyaxial head (2) thus has adetermined clearance around at least one axis not parallel to the axis(A₁) of symmetry of the osseous anchoring means (11). This clearance isdue to the fact that the head (2) is free in rotation around the axis(A₁) of the body (1), in rotation around the axis (A₂) of the head (2),substantially perpendicular to the axis (A₁) of the body (1) of theimplant, and in rotation around the axis (As), substantiallyperpendicular to the axes (A₁) of the body (1) and (A₂) of the head andparallel to the axis (A₄) of the duct. This freedom of rotation of thehead (2) around these axes (A₁, A₂ and A₅) allows a determined clearanceof the head (2), in whatsoever direction, around osseous anchoring meansnotably constituted of the body (1) of the implant. This clearanceallows the head (2), in the absence of the fixation bar (7), to follow acircular ring centered on the olive (3) and bearing a shapesubstantially identical to the external surface of the olive (3) andtherefore take whatsoever position in this ring, in relation to theolive (3). The head (2) is equipped with a lateral aperture (23)allowing to introduce the bar via the side of the duct (20). The head(2) also comprises a channel (22) of axis (A₃), not parallel (forexample substantially perpendicular) to the axis of the duct (20). Thischannel (22) is threaded so as to receive a fixation screw (5) of thebar (7). The head (2) is also equipped, on the other side of the latterin relation to the duct (20), of a ring (21) whose internal surface isconcave, smooth and complementary of the convex and smooth external wallof the fixation olive (3). In relation to the bar (7), the internalsurface of the duct (20) is sufficiently large to allow some clearanceof the bar (7) in the duct (20).

According to an embodiment of the invention, the fixation screw (5) ofthe bar bears, at its end located on the side of the bar (7), a mobileand articulated element, called ball and socket (52), as that describedin the international patent application WO 03/049629 filed by theapplicant. The ball and socket (52) consists in a sphere portion (theball) inserted into a housing (the socket) in the lower end of thefixation screw (5) whose shape is complementary of the sphere portion ofthe ball and socket (52). This complementary nature of the shape ensuresa ball and socket connection between the fixation screw (5) and the bar(7). The ball (52) can have a flat (520) at its base. The bar (7) canalso have a flat (71), complementary of the flat (520) at the base ofthe ball (52), so as to allow a better fixing of the bar (7) whenscrewing the fixation screw (5) of the bar. This mobile link authorizessome clearance of the ball (52) in relation to the fixation screw (5),in rotation around the center of this ball and socket (52). This balland socket connection also allows the flat (71) of the bar (7) to remainin contact with the flat (520) of the ball and socket (52) withoutslippage, which avoids deteriorating the surfaces in contact, rendersthe blocking more reliable, and reduces the risks of residual stress. Inaddition, the flat (520) of the ball (52) can consist, as represented onFIGS. 5b, 6a and 6b , in a disc (520) prominent at the periphery of thebase of the ball (52). The fact that this disc (520) is prominent at theperiphery of the base of the ball (52) and thus protruding in the duct(20) makes it possible to use it as a stop limiting the rotation of theball (52) in its socket (thus limiting the rotation of the ball inrelation to the fixation screw). For instance, the disc (520) can beplaced as a stop in the internal surface of the duct (20), on the sideopposite to the one where the lateral aperture (23) is. This placementof the disc (520) as a stop prevents the rotation of the bar (7) aroundthe axis (A₄) of the duct (20), thanks to the contact between the disc(520) of the flat at the base of the ball (52) and the flat (71) of thebar (7). The corresponding rotation of the head (2) around the axis (A₅)is thus also prevented and it prevents the descending of the head (2) inrelation to the bar (7). The ball and socket connection (52) can beassociated with a widening of the duct (20) whose ends have a diametergreater than that at the center of the duct (20), as particularlyvisible in FIG. 5c . The bar (7) is thus fixed between the ball andsocket (52) and the central part of the duct (20), but has a freedom ofmovement around its longitudinal axis (A₄). This freedom of movement cannaturally consist in a rotation of the bar (7) around the axis (A₃) ofthe duct (22) and/or a rotation of the bar (7) around the axis (A₄) ofthe duct (20) and/or a rotation of the bar (7) around an axis parallelto the axis (A₂) and passing through the point of intersection betweenthe axes (A₃) and (A₄). The ball and socket connection (52) at the baseof the fixation screw (5) therefore allows a determined clearance of thebar (7) around at least one axis (A₄) parallel to the axis of the duct.This clearance allows the bar to follow a conical course with, for itssummit, the point of intersection between the axes (A₃) and (A₄) (thatmeaning, for example, the center of the duct) and bearing an acute angleat its summit.

In an alternative of the embodiment, the ball and socket (52) can beassociated with a mobile base (6) placed between the bar (7) and theduct (20). The base (6) is mobile compared to the fixation head (2) andhas on its upper face, called support face (62), in contact with the bar(7), a shape complementary of the external surface of this bar (7), forexample in the form of a cylinder portion, which provides a good contactsurface when tightening the fixation screw (5) of the bar. This mobilebase (6) has a part (61) in the shape of a sphere portion, leaning via acomplementary contact in a housing formed in the wall of the duct (20).By virtue of this spherical contact, the mobile base (6) has somefreedom of rotation around the center of its spherical part (61). On itspart (61) in form of a sphere portion the mobile base (6) can have oneor a plurality of irregularities (610) in its shape co-operating withone or a plurality of irregularities in the shape of its housing in theduct (20) of the fixation head (2), so as to form a stop limiting theclearance in rotation of the mobile base. These irregularities (610) canbe, for example, a pin protruding from the mobile base and co-operatingwith a larger dimensioned cavity formed on the complementary contactsurface. On the contrary, the pin can be in the head (2), at the housingin the duct (20), and protruding into this housing so as to co-operatewith a larger dimensioned cavity in the base (6), as for example the pinformed by the screw shown in FIG. 6b , fixed in the head (2), at thehousing in the duct (20). This stop, for example, allows avoidingexcessive turning of the mobile base (6) and assuring that it properlypresents its support facing the bar (7). Just as when the ball andsocket (52) is associated with a widening of the duct (20), the bar (7),clamped between the ball and socket (52) and the mobile base (6), has afreedom of movement around its longitudinal axis (A₄), in any direction,for example by a combination of rotations around the axes described forthe above alternative of the embodiment. The embodiment alternativeincluding the mobile base (6) additionally allows that this freedom ofmovement is restricted thanks to the irregularities (610) co-operatingwith the irregularity (or irregularities) of the housing in the duct(20) of the head (2).

Thus, it can be understood that the bar (7) can be inserted and blockedin different angular positions inside the duct (20), while providing aflat contact surface both with the fixation screw, possibly includingthe ball and socket (52) and with a part of the wall of the widened outduct (20) or with the support face (62) of the mobile base (6). It canalso be understood that the invention has the advantage of providingdifferent elements of the implant with a complete freedom of movement inrelation to one another. Indeed, the head (2) has, as previouslyindicated, a freedom of movement around the center of the olive (3) andthe bar (7) has a freedom of movement around, for example, the center ofthe duct (20), thanks to angular clearances by rotation around the axesrepresented in FIG. 2. Thus, all the possible levels of freedom arereached for the position of the head (2) in relation to the body (1) ofthe implant and for the bar (7) in relation to the duct (20) of the head(2). The combination of these levels of freedom of the head and of thebar provide the implant of the present invention with the advantage ofallowing a clearance, in every direction, of the bar (7) in relation tothe body (1) of the implant. In particular, even when the bar (7) isinserted into the duct (20) of the head (2), the position of the bar (7)can be adjusted, for example, thanks to a rotation of the head aroundthe axis (A₁) of the body of the implant and a rotation of the barsubstantially around the axis (A₃) of the channel (22) of the fixationscrew. These possible rotations are particularly interesting for thereduction of a spondylolisthesis, because the natural movement of avertebra during this reduction is substantially circular. It is thus ofparticular interest to provide the implant with a freedom of movementduring the reduction. Only an implant as the present invention,combining a polyaxial head (2) with a ball and socket (52), allows thisfreedom of movement facilitating the reduction of the spondylolisthesis.Even when the bar (7) is inserted into the duct (20), the inventionallows for a determined clearance of the head (2) around the axis ofsymmetry (A₁) of the osseous anchoring means. This clearance allows thehead (2) to follow a conical course, if the bar (7) inserted into theduct (20) is not fixed, a cone whose base has a perimeter in the shapeof a disc or ellipse, whose summit is located at the center of the olive(3) and which has an acute angle at its summit. The different angularclearances allow to insert the bar (7) into the head (2) with greaterease and to obtain a tightening of the bar in its most natural positionin relation to the implants, which reduces or cancels out the stressesthat could remain in the device after tightening. Moreover, thetightening efforts converge in this way directly to the blocking withouthaving to conflict with the rigidity of the bar, and the reliability ofthe blocking is therefore improved. The bar is fixed to the head (2) viascrewing of the fixation screw (5) in the channel (22) once the bar isin the desired position. The fixation olive (3) is constituted of a ringwith a tapered and smooth internal wall, complementary of the smoothtapered part (12) of the body (1) of the implant. The external wall ofthe olive (3) is convex and complementary of the internal surface of thefixation ring (21) of the head (2). The olive (3) is sectioned at apoint (30) of the ring, along the entire height of the latter. Theminimum diameter of the tapered internal wall of the ring is slightlygreater than the external diameter of the cylindrical part (10) of thebody of the implant, so that the cylindrical part (10) of the body (1)of the implant can be threaded into the olive. The olive (3) is insertedinto the fixation ring (21) of the head (2) by applying pressure to theolive (3) which compresses thanks to the section made along its height,to allow its insertion into the ring (21), then by releasing thepressure on the olive (3) so as to allow it to dilate in the ring (21).The positioning and the retaining of the olive (3) in the ring (21) isthus done automatically thanks to the complementary nature between itsconvex external wall of the olive (3) and the concave internal surfaceof the ring (21) and thanks to the fact that the olive has an externaldiameter slightly smaller than the internal diameter of the ring.

The nut (4) comprises at its center, and along its height, a threadedcylindrical drilling (40), of internal diameter substantially equal tothe external diameter of the cylindrical part (10) of the body (1) ofthe implant. The nut (4) comprises on its external wall a plurality offlats (41) allowing to screw the nut (4) to the cylindrical part (10) ofthe body of the implant using an adapted tool, for example a monkeywrench.

In a first embodiment represented in FIGS. 1 and 2, the anchoring means(11) of the body (1) of the implant are an extended part comprising athread, which is intended to be screwed into the osseous matter, forexample at the pedicle or the body of a vertebra, or in the sacrum. Tofacilitate the installing of the body (1) of the implant, the upper partof the cylindrical part (10) of the body (1) of the implant is fittedwith a blind hole (13) with six faces, which is of a complementarynature of a known screwing tool of the implant. It is to be noted thatthanks to the drilling (40) performed along the entire height of the nut(4), this blind hole (13) remains accessible for screwing of the osseousanchoring means (11), even when the nut (4) is inserted on thecylindrical part (10) of the body (1) of the implant.

In a second embodiment represented in FIGS. 3 and 4, the anchoring means(11) of the body (1) of the implant are a hook, intended to be hookedonto a formal irregularity of the osseous element, such as a pedicle, ablade or a vertebrae transversal apophysis.

As aforementioned, the fixation olive (3) is inserted into the ring (21)of the head (2) and stays automatically retained there thanks to thecomplementary nature between the shape of the convex external surface ofthe olive (3) and the concave internal surface of the ring (21). Thefixation olive (3) and the head (2) are threaded to the cylindrical part(10) of the body (1) of the implant, as far as the tapered part (12) ofthe body, complementary of the tapered internal surface of the olive(3). The nut (4) is partially screwed onto the cylindrical part (10) ofthe body (1) of the implant, so as to retain the head (2) and thefixation olive (3) on the cylindrical part (10) of the body (1) of theimplant, whilst maintaining their freedom of movement. Thus, the head(2) can be orientated in any given direction, thanks to its rotationaround the aforementioned axes (A₁, A₂ and A₅). At this stage, thedifferent elements of the implant do not need to be integrally retainedbetween themselves as the olive (3) automatically holds in the ring (21)and on the tapered part (12) of the body (1). The head (2) willtherefore be spontaneously vertically stable compared to the body (1) ofthe implant, only its orientation, according to the different possibleangular clearances, requires a screwing of the nut (4) in order to bestabilized. As aforementioned, the blind hole (13) with six faces,allowing the screwing of the body (1) of the implant, remains accessibleeven when the nut (4) is threaded onto the threaded part (10) of thebody (1), the relative vertical stability of the unit made of the headand the olive on the body of the implant will allow to screw the body(1) of the implant driving the head and the olive. When the bar (7) isfixed, the screwing of the nut (4) on the threaded part (10) of the body(1) of the implant will allow, thanks to this relative stability of thehead and the olive in relation to the body, either the rise (theascension) of the body of the implant if the latter was too low comparedto the bar (7), or the lowering of the olive and the head on the body ifthe first elements were too high compared to the latter and the bar (7).Then the screwing of the nut provokes the contact of the olive on thetapered part (12) of the body engendering the dilating of the olive andthe blocking of the head according to the desired orientation.

The implant according to the invention is particularly useful forreducing the jutting out of a vertebra of the rachis compared to a firstvertebra.

In a first embodiment of the method for installing the implant such asrepresented in FIGS. 1 and 2, the body (1) of the implant, fitted withthe fixation olive (3) the head (2) and the nut (4), is screwed into thejutting out vertebrae until the duct (20) arrives substantially at thesame level as a bar (7) already fixed in another implant previouslyfixed to the first vertebrae. The bar (7) is then inserted into the duct(20) of the head (2) via the lateral aperture (23) and is retained inthe duct (20) via a partial screwing of the fixation screw (5) in thechannel (22) of the head (2). The disc (520) of the flat at the base ofthe ball (52) is placed at the contact of the flat (71) of the bar (7)and as a stop in internal surface of the duct (20) of the head (2), onthe opposite side lateral aperture (23), so as to prevent the lowering(i.e., descending) of the head (2) in relation to the bar (7). Anotherpossibility for preventing the descending of the head (2), via arotation of the bar (7) around the axis (A₄) and an associated rotationof the head (2) around the axis (A₅), consists in a complete screwing ofthe fixation screw (5) which will then prevent any possible rotation ofthe ball (52) in its socket. Nevertheless, as aforementioned, thenatural movement of a vertebra during the reduction of aspondylolisthesis necessitate a freedom pf movement of the implant,particularly a freedom of rotation of the head (2) around the axis (A₁)of the body (1) and a freedom of rotation of the bar (7) around the axis(A₃) of the channel (22). It is thus better to prevent the lowering ofthe head (2) by placing the ball (52) as a stop in the duct (20), so asto allow the rotations of the head (2) and the bar (7) around their twoother possible axis. The method continues with the partial screwing ofthe nut (4) on the cylindrical part (10) of the body (1) of the implant,so that it comes into contact with the fixation olive (3). In thismanner, the vertical position of the head (2) is retained in relation tothe body (1) of the implant whilst allowing the movement of the head (2)in relation to the body (1) of the implant, around the axes (A₁), (A₂)and (A₅). The head (2) and the fixation olive (3) can not be disengagedfrom the cylindrical part (10) of the body (1), even if a downward forceis applied to the body (1). The method continues with the screwing ofthe body (1) of the implant in the jutting out vertebra, thanks to theblind hole (13) with six faces. The head (2) of the implant beingsubstantially motionless in the vertical position compared to the bar(7), thanks to the disc (520) of the ball placed as a stop, the tractiondue to the screwing of the osseous anchoring means (11) of the body (1)engenders the correcting of the jutting out vertebra, thanks to the riseof the body (1) along its axis (A₁), whilst the olive (3) and the head(2) stay vertically stable in relation to the bar (7). The vertebra cannow be returned to a level chosen by the person implementing the method,which is no more than the same as the first vertebra. The reduction of aspondylolisthesis is generally more difficult at the end of its coursethan at the beginning. The screwing of the osseous anchoring means (11)coming with a reduction of the jutting out of a vertebra may thus becomemore and more difficult while the jutting out is reduced. The reductionthus includes a risk of a tearing out of the osseous anchoring means(11) from the vertebra. Thus, at the end of the reduction, it is betterto screw the nut (4) than the osseous anchoring means (11), in order toend the rise of the body (1) and the vertebra. Then, when the vertebrahas been brought back to an appropriate level, the head (2) is fixed tothe body (1) of the implant via complete screwing of the nut (4) on thecylindrical part (10) of the body of the implant, which engenders thepushing of the fixation olive (3) towards the tapered part (12) of thebody (1) of the implant. Under this pressure, the fixation olive (3)undergoes an expansion when its tapered and smooth internal wall startsto come into contact with the tapered part (12) of the body (1) of theimplant. The head (2), whose ring (21) clasps the fixation olive (3), isthen blocked in the desired position, the internal diameter of the ring(21) being slightly greater than that of the fixation olive (3). If ithas not already been, the bar is then fixed to the head (2) of theimplant via complete screwing of the fixation screw (5) in the channel(22) of the head (2).

In a second embodiment of the method for installing the implant such asrepresented in FIGS. 1 and 2, the body (1) of the implant fitted withthe fixation olive (3), the head (2) and the nut (4), is screwed intothe jutting out vertebrae until the duct (20) arrives substantially atthe same level as a bar (7) already fixed in another implant previouslyfixed to the first vertebrae. The bar (7) is then inserted into the duct(20) of the head (2) via the lateral aperture (23) and is at leastretained via screwing of the fixation screw (5) in the channel (22) ofthe head (2). As aforementioned, the disc (520) of the flat at the baseof the ball (52) can be placed at the contact of the flat (71) of thebar (7) and as a stop in internal surface of the duct (20) of the head(2), on the opposite side lateral aperture (23), so as to prevent thelowering (i.e., the descending) of the head (2) in relation to the bar(7). This lowering can also be prevented by a complete screwing of thefixation screw (5), so as to block the ball and socket (52) and thusprevent the rotation of the bar (7) in the duct, because of the contactbetween the flat (71) of the bar (7) and the flat (520) of the ball(52). We then continue to screw the body (1) of the implant into thejutting out vertebrae to lower it by a distance chosen by the personimplementing the method, and which corresponds to no more than the gapof the jutting out vertebrae compared to the first vertebrae. The nut(4) is then completely screwed down, which results in rising theimplant, and therefore the jutting out vertebrae, by the distancetravelled by the implant once the bar (7) was introduced in the duct(20) of the head, therefore moving it said distance. This embodiment ofthe method can be chosen when the initial jutting out of the vertebra isnot very big and the length of the cylindrical and threaded part (10) ofthe body is sufficient for reducing the spondylolisthesis. Thisembodiment has the advantage to limit the risks of tearing out theosseous anchoring means (11) from the vertebra since their screwing inthe osseous matter is performed in the absence of the constraints due tothe vertical stability of the head (2). As long as the nut (4) is simplyin contact with the fixation olive (3), this correcting of the vertebraeis performed by the fraction produced by the bar (7) on the head (2)under the effect of the screwing of the nut (4), thanks to the stabilityof the olive (3) and therefore of the head (2), in relation to the body(1), thanks to the contact between the flat (71) of the bar (7) with thestop formed by the disc (520) of the ball, as aforementioned. Thescrewing of the nut (4) thus corrects the position of the vertebra andthe body 0, via rising of the body (1) along its axis (A₁), whilst theolive (3) and the head (2) stay vertically stable in relation to the bar(7) and then engenders the fixing of the head (2) onto the body (1) ofthe implant via expansion of the fixation olive (3) which produces theblocking of the head (2) in the desired position. If it has not alreadybeen, the bar (7) is then fixed to the head (2) of the implant viacomplete screwing of the fixation screw (5) in the channel (22) of thehead (2).

In a third embodiment of the method for installing the implant such asrepresented in FIGS. 3 and 4, the body (1) of the implant, fitted withthe fixation olive (3), the head (2) and the nut (4), is hooked to aformal irregularity of the jutting out vertebrae, thanks to the hook ofthe body (1) visible in FIGS. 3 and 4. The bar is then inserted into theduct (20) of the head (2) via the lateral aperture (23) and is at leastretained, even fixed, via screwing of the fixation screw (5) in thechannel (22). The method continues with the screwing of the nut (4),which results in rising the body (1) of the implant, and thus thejutting out vertebrae, by moving it to a level chosen by the personimplementing the method, which is no more than the first vertebrae, andas long as the nut (4) is simply in contact with the fixation olive (3),then engenders the fixing of the head onto the body (1) of the implantvia expansion of the fixation olive (3) which produces the blocking ofthe head (2) in the desired position. If it has not already been, thebar is then fixed to the head (2) of the implant via complete screwingof the fixation screw in the channel (22) of the head (2).

In these three embodiments of the method, the raising of the jutting outvertebrae to a level chosen by the person implementing the method,performed according to a curve, the polyaxiality of the connectionbetween the body (1) of the implant and the head (2), via thepossibility of rotation around the axes (A₁), (A₂) and (A₅), is thenentirely suitable. If the fixation screw (5) does not comprise a flat atits base but instead a ball and socket (52), possibly associated to amobile base (6) placed between the bar (7) and the duct (20), theimplant is provided with a double polyaxiality allowing to furtherreduce the stresses on both the rachis and the bar, thanks to thepossibilities for rotating the head (2) around the axes (A₁), (A₂) and(A₅), even when the bar (7) is inserted in the duct (20) of the head(2).

It should be clear to the specialist in the art that the presentinvention enables embodiments in many specific forms without moving itaway from the field of application of the invention as claimed.Consequently, the present embodiments must be considered asillustrative, but can be modified in the field defined by the import ofthe attached claims and the invention should not be limited to thedetails provided above.

The invention claimed is:
 1. An osseous anchoring implant comprising: abody comprising an osseous anchor with an anchor axis at a first end ofthe body, a threaded cylindrical part disposed at a second end of thebody at the opposite end of the anchor axis from the first end of thebody, and a tapered part integral with the body disposed between theosseous anchor and the threaded cylindrical part; a fixation olivehaving a tapered internal wall configured to rest on the tapered part ofthe body; and a head comprising a duct having a duct axis and a lateralaperture configured to receive an osteosynthesis bar via a side of theduct, the duct having ends separated along the duct axis and a centerdisposed along the duct axis between the ends of the duct, with the ducthaving internal diameters at the ends that are greater than an internaldiameter of the duct at the center, a threaded fixation screw comprisinga ball and socket disposed at an end of the fixation screw, a threadedchannel having a channel opening into the duct and a channel axis notparallel to the duct axis, the treaded channel being configured to holdthe fixation screw with the ball and socket at least partially disposedin the duct, a mobile base disposed in the duct opposite the channelopening, the mobile base having a support face in the form of cylinderportion protruding at least partially into the duct, and a fixation ringconfigured to receive the fixation olive and mount the head to the body;the osseous anchoring implant having an installation configuration inwhich the fixation olive is threaded onto the threaded cylindrical partand disposed at a first distance from the second end of the body, and aninstalled configuration in which the tapered internal wall of thefixation olive is in contact with the tapered part of the body and thefixation olive is disposed at a second distance from the second end ofthe body, with the first distance less than the second distance.
 2. Theosseous anchoring implant of claim 1 further comprising a osteosynthesisbar having a length and a flat surface extending along the length. 3.The osseous anchoring implant of claim 1, in which the fixation ring isintegral with the head and disposed on an opposite side of the head fromthe duct, the fixation olive is sectioned along its entire height, andthe cylindrical part of the body is threaded.
 4. The osseous anchoringimplant of claim 2 in which the flat surface extending along the lengthof the osteosynthesis bar does not extend to at least one end of theosteosynthesis bar.
 5. The osseous anchoring implant of claim 3, furthercomprising a nut comprising a threaded bore co-operative with thethreaded cylindrical part of the body to press the fixation oliveagainst the tapered part of the body when the nut is tightened.
 6. Theosseous anchoring implant of claim 5, in which the nut has flatsco-operative with a tool adapted to screw the nut.
 7. The osseousanchoring implant of claim 1, in which the osseous anchor is a hook. 8.The osseous anchoring implant of claim 1, in which the osseous anchor isthreaded.
 9. The osseous anchoring implant of claim 8, in which an endof the extending part of the body has a recess configured to co-operatewith a tool for rotating the body.
 10. The osseous anchoring implant ofclaim 1, in which the ball and socket comprises a flat base.
 11. Theosseous anchoring implant of claim 10, in which the flat base of theball and socket is disposed on a disc.
 12. The osseous anchoring implantof claim 4 in which the ball and socket comprises a flat base and theosteosynthesis bar comprises a surface forming a cylinder portionextending along the length of the osteosynthesis bar, and the osseousanchoring implant has a configuration in which the osteosynthesis bar isfixed in the duct with: the flat base of the ball and socket fixed bythe threaded fixation screw against the flat surface extending along thelength of the osteosynthesis bar, a portion of the surface of theosteosynthesis bar forming a cylinder portion fixed against the supportface of the mobile base, and the length of the osteosynthesis baroriented in the duct at an angle with the duct axis.
 13. The osseousanchoring implant of claim 1, in which the mobile base hasirregularities in its shape, co-operative with irregularities in thehousing formed in the duct to restrict the movement of the mobile basein the housing.
 14. An osseous anchoring system comprising: an implantcomprising a body comprising an osseous anchor disposed at a first endof the body, a threaded cylindrical part disposed at a second end of thebody, and a seat disposed between the osseous anchor and the threadedcylindrical part, a fixation olive comprising an internal wall, and ahead comprising a duct having a duct axis and a lateral apertureconfigured to receive an osteosynthesis bar via a side of the duct, theduct having ends separated along the duct axis and a center disposedalong the duct axis between the ends of the duct, with the duct havinginternal diameters at the ends of the duct that are greater than aninternal diameter of the duct at the center, the duct comprising firstand second walls that taper from the ends of the duct toward the centerof the duct and join at a third wall disposed in the center of the duct,a threaded fixation screw comprising a ball and socket disposed at anend of the fixation screw, the fixation screw being translatable in achannel having an opening in duct that is on an opposite side of theduct from the third wall of the duct, and a fixation ring configured toreceive the fixation olive and mount the head to the body; and a bar,the bar having a blocked configuration in which the bar is blocked inthe duct with a first side of the bar pressed against the ball andsocket and with a second side of the bar opposite the first side of thebar pressed against one of the first, second, and third walls of theduct, with the osseous anchoring system having an installationconfiguration in which the fixation olive is threaded onto the threadedcylindrical part and disposed at a first distance from the second end ofthe body, and an installed configuration in which the internal wall ofthe fixation olive is in contact with the seat and the fixation olive isdisposed at a second distance from the second end of the body, with thefirst distance less than the second distance.